Intravascular diseases are commonly treated by relatively non-invasive techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA). These therapeutic techniques are well known in the art and typically involve the use of a balloon catheter with a guide wire, possibly in combination with other intravascular devices. A typical balloon catheter has an elongate shaft with a balloon attached proximate the distal end and a manifold attached to the proximal end. In use, the balloon catheter is advanced over the guide wire such that the balloon is positioned adjacent a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened.
There are three basic types of intravascular catheters for use in such procedures including fixed-wire catheters, over-the-wire (OTW) catheters and single-operator-exchange (SOE) catheters. The general construction and use of FW, OTW and SOE catheters are all well known in the art.
Several characteristics that are important in intravascular catheters include pushability, trackability and crossability. Pushability refers to the ability to transmit force from the proximal end of the catheter to the distal end of the catheter. Trackability refers to the ability to navigate tortuous vasculature. Finally, crossability refers to the ability to navigate the balloon catheter across narrow restrictions in the vasculature.
To maximize pushability, some prior art catheters incorporate a stainless steel outer tube (also referred to as a hypotube) on the proximal shaft section and a polymeric distal shaft section. One limitation of such a construction is that hypotubing is often prone to kinking. To reduce the likelihood of kinking, some prior art catheters use a relatively stiff polymer (e.g., composite) or reinforced polymer in the proximal shaft section.
The trackability of a particular catheter design is analyzed in terms of the trackability of the distal portion of the catheter, as this portion must track the guidewire through small tortuous vessels to reach the stenosed area to be treated. A more flexible distal portion has been found to improve trackability. Therefore, to maximize pushability, the catheter should have a relatively stiff proximal section. To maximize trackability, the catheter should have a relatively flexible distal section.
A limitation of this basic structure is that kinking can occur at the joint between the relatively stiff proximal shaft section and the relatively flexible distal shaft section. To reduce the likelihood of kinking, some prior art catheters use one or more tubular sections of intermediate flexibility between the relatively stiff proximal section and the relatively flexible distal section to provide a more gradual transition in flexibility therebetween. While this approach provides some benefit, the resulting transition in flexibility is often step wise, and can still be susceptible to kinking at the junctions of the various intermediate sections.
It would be desirable, therefore, to provide an intravascular catheter that has a more gradual transition in flexibility along its length.